Due to an aging society, it has been desired to develop an orally rapidly-disintegrating tablet which can be easily taken by patients having difficulty in swallowing tablets such as elderly people and also children. Furthermore, it is useful to develop an orally rapidly-disintegrating tablet not only for elderly people or children but also for other patients because of the convenience of an orally rapidly-disintegrating tablet (i.e. an orally rapidly-disintegrating tablet can be taken without water).
However, there is a problem in using an orally rapidly-disintegrating tablet in the same manner as ordinary tablets because it is difficult to maintain the hardness of an orally rapidly-disintegrating tablet after taken out from the package. In the conventional art, there seems to be no disclosures about the hardness, or even if there are, such disclosures merely describe how hard an initial hardness of a tablet needs to be in case that the tablet is taken out from the package. There seems to be no disclosure teaching that the hardness of the tablet would decrease after taken out from the package. An orally rapidly-disintegrating tablet is required to have a short disintegration time in the oral cavity, and a suitable hardness to prevent the tablet from being chipped or powdered in manufacturing or transporting the tablet. However, hardness and disintegration time are conflicting factors, and in general, when disintegration time is shortened, hardness will be decreased, and when hardness is increased, disintegration time will be expanded. In order to solve the problem of the two conflicting factors (i.e. disintegration time and hardness), it is known to use processes such as wet compression methods and heat compression methods. However, the problem is that the said methods cannot be carried out with typical equipments for compressing/shaping formulations, and the said methods require special equipments such as warming devices, humidification devices, and drying devices.
Furthermore, it is known to add an additive agent to the orally rapidly-disintegrating tablet as a different means in order to solve the above-mentioned problem. As an example of such additive agent, Patent Reference 1 discloses a composition for pharmaceuticals which can be obtained by homogeneously dispersing an inorganic compound and a saccharide to give a suspension, and then spray-drying the suspension. Patent Reference 2 discloses a composition which can be obtained by spray-drying a suspension of a saccharide (i.e. a combination of mannitol and xylitol), an inorganic excipient and a disintegrant; and also discloses an orally rapidly-disintegrating tablet comprising the composition. Patent Reference 3 discloses an orally rapidly-disintegrating tablet which comprises a step of using a disintegrating agent at the final stage of the formulation process.
Meanwhile, not a few medicaments have “unpleasant taste” which have, for example, a bitter taste, an astringent taste, and a pungent taste. When such medicament is contained in the orally rapidly-disintegrating tablet and dissolved in the oral cavity, it is often difficult to take the tablet. In particular, Patent Reference 4 describes a technique to formulate an orally rapidly-disintegrating tablet with such “medicament with unpleasant taste”, which improves the unpleasant taste of the medicament by mixing a medicament with unpleasant taste, methylcellulose and mannitol, and then particulating the mixture.    [Patent Reference 1] JP 2000-086537 A    [Patent Reference 2] JP 2005-139168 A    [Patent Reference 3] WO 2007/029376    [Patent Reference 4] WO 2005/055989